The underfloor vehicle lifting jack is used for examination and repair of motor train units, high-speed trains, high-power locomotives or urban rail vehicles which are intact and not dismantled, including replacement of bogies for railway vehicles, examination and repair and replacement of electric installations at the bottom and top of the vehicle bodies, etc. With large-scale use of motor train units and high-speed trains in China, the underfloor vehicle lifting jack for motor train units plays an important role in high-level examination and repair of trains. For unwheeling of a motor train unit, firstly the entire train is synchronously lifted to a certain height by a bogie lift unit and the bogie is disassembled, then the railway carriage is propped up by a vehicle body lift unit.
In the process of unwheeling, both the lift pillar and the propping head part of the vehicle body lift unit elevate above the soil, hence the cover plate at ground level is provided with corresponding openings, which are not only inconvenient for examination and repair, but also bring hidden danger for personal safety of maintainers. Frequently, an inverting cover plate apparatus is used in order to block off these openings without influencing stretching and retraction of the vehicle body lift pillar. A conventional inverting cover plate has the following two structures: (1) the inverting cover plate is directly jacked up by the vehicle body lift unit, and the guide wheel on the inverting cover plate jacked up rolls along the lift pillar; this type of cover plate is applicable in the case that the propping head is basically parallel and level to the lift pillar, but not applicable in the case that the propping head is comparatively long. (2) a per pale inverting cover plate, the inverting cover plate of this structure takes up a large space, thus reducing the space for examination and repair, which is inconvenient for examination and repair of vehicles lifted.